A southern right whale and calf breach the ocean surface near South Africa, in this undated photo.

A recent study indicates that a semiaquatic, raccoon-size mammal called Indohyus represents the ''missing link'' in the evolution of whales.

The structure of the animal's skull and ear show Indohyus was closely related to whales, the study team said, adding that the density of its bones and the chemistry of its teeth suggest it spent much of its time in the water.

But the crucial piece of evidence that would link the animal to whales is the ear bone covering the animal's middle ear, said Philip D. Gingerich, a University of Michigan paleontologist. Full analysis of the ear is missing in the new paper, he said.

Gingerich thinks that more convincing information is needed than what is provided in the study.